Challenger Martin Schulz of the centre-left Social Democratic Party (SPD) is leading his campaign with "more social justice", promising reforms to tax, unemployment benefits and childcare after having just succeeded with a push to legalize same-sex marriage.
Merkel's centre-right Christian Democratic Union (CDU) has so far failed to counter its opponents' focused campaign with a unifying policy theme of its own.
Social media users last week mocked party secretary-general Peter Tauber's slogan "For a Germany where we live well and gladly", after he transformed the initial letters of the German phrase into an unpronounceable Twitter hashtag: #fedidwgugl.
Schulz, struggling to catch up with Merkel in the polls, last week shocked observers by accusing the chancellor of systematically refusing to debate him on the future of the country.
But the lacklustre CDU campaign does not appear to have hurt the re-election prospects of the veteran leader dubbed "Mutti" (Mummy) by German voters.
'Germany in good hands'
After a brief spell between January and March when Schulz, a newcomer on the German political landscape, surged into the lead, the former European Parliament president has fallen far behind Merkel as the preferred candidate in polls by public broadcaster ARD.
Rallying around a trusted leader is a long tradition for the CDU, whose simple "No experiments!" campaign posters for Konrad Adenauer's reelection in 1957 remain a touchstone of German political culture.
Angela Merkel and Horst Seehofer. Photo: DPA
Merkel's mentor, recently-deceased former chancellor Helmut Kohl, was accused of transforming the CDU into a "chancellor electing society" during his 16-year reign.
And Merkel herself echoed the strong-leader theme in 2013, with gigantic posters featuring her fingers clasped and the slogan "Germany in good hands".
Merkel's government faced heavy pressure in 2015 when it opened the nation's borders to a mass influx of refugees, sparking a xenophobic backlash.
But as the arrivals have slowed sharply, the issue has faded from public debate, as the upstart anti-immigration Alternative for Germany party slipped back into single digits in the polls.
Tax cuts and families
The few concrete policies that have filtered out from the CDU party machinery, and their Bavarian CSU allies, are familiar to conservatives the world over.
The sister parties plan to lower income taxes, increase the threshold for the highest bracket and wind down so-called "solidarity surcharges" introduced after Germany's 1990 reunification to pay for government spending on the former communist East Germany, news agency DPA reported last week.
Lower taxes favouring higher consumer spending and thereby increased imports could also be seen as a gesture to foreign critics of Germany's massive trade surplus.
While US President Donald Trump has made the bluntest attacks on the imbalance, experts at the International Monetary Fund as well as European allies like France have all called on Germany to reduce it.
Finance Minister Wolfgang Schäuble has suggested there is room for around €15 billion ($13.1 billion) of income tax cuts.
That figure is unlikely to satisfy the government's critics at home or abroad when compared with the €1.35 trillion in taxes and social contributions collected by Germany's federal, state and municipal governments last year.
Other local media have reported on CDU/CSU plans to increase benefits and tax relief for families with children, improve primary schools and daycare, and accede to a longstanding industry demand to exempt research and development spending from taxes.
Only one major issue, an echo from the refugee crisis, continues to divide Merkel from the more conservative Bavarians: whether Germany should set an upper limit on the number of refugees allowed to enter the country each year.
By Tom Barfield